The present invention relates to the field of treating the ground by vibration compacting.
The vibration compacting technique consists in causing a penetration unit to penetrate vertically into the ground, which unit comprises a vibrator device connected to a carrier via a plurality of tubes having substantially the same diameter as the vibrator device.
When the penetration unit penetrates into the ground, the vibrator device generates radial vibration that diffuses through the ground, with the effect of improving its mechanical properties. For example, the technique is used for compacting a volume of ground that is constituted, for example, of grains, such as sand.
More precisely, the invention relates a vibrator device for a vibration compacting machine, said device comprising:                a tubular body extending longitudinally while presenting a bottom end;        at least a first hydraulic motor disposed in the tubular body and comprising a rotor rotatably mounted in a stator-forming casing; and        an eccentric member arranged inside the tubular body between the bottom end and the first hydraulic motor, said eccentric member being designed to be driven in rotation by the rotor of the first hydraulic motor in order to produce vibration.        
The hydraulic motor fitted to such a vibrator device comes from a conventional commercially-available range of motors.
The motor used in the prior art consists of a rotor and a stator that form an assembly that is distinct from the other elements of the vibrator device, and in particular from the tubular body.
During assembly, the motor assembly is placed in the tubular body in order to connect the eccentric member to the rotor. Conventionally, the rotor is the portion of the motor that is mounted to rotate in the casing of the motor.
Such vibrators are described in particular in Documents US 2002/003989 and DE 102 32 314, in which the motor assembly constitutes a unit that is distinct from the remainder of the vibrator device, and in particular from the tubular body.
A drawback of that configuration is that it makes it necessary to use hydraulic motors of small cylinder capacity, and thus presenting low power.
One of the constraints on vibrator devices is that they must penetrate easily into the ground. To do this, it is desirable to minimize the diameter of the tubular body. Penetration into the ground is made easier by a tubular body that is fine.
That is why it is desired to build vibrator devices that present a diameter that is as small as possible, typically of the order of 300 millimeters (mm).
As a result, the volume available for the hydraulic motor is limited. The penetration capacity of the vibrator device is thus generally obtained to the detriment of the power of its hydraulic motor.
It is why certain manufacturers are discarding the hydraulic solution and prefer to use an electric motor having component elements that can present a length that is longer relative to their diameter.